8-Speed Transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets having six torque-transmitting mechanisms, two fixed interconnections and a grounded member. The powertrain includes an engine and torque converter that is selectively connected to at least one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting mechanisms provide interconnections between various gear members, the transmission housing and with the input member, and are operated in combinations of three to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having threeplanetary gear sets that are controlled by six torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission having three planetary gear sets controlled to provideeight forward speed ratios and one reverse speed ratio.

The electrically variable transmission family of the present inventionhas three planetary gear sets, each of which includes a first, secondand third member, which members may comprise a sun gear, a ring gear, ora planet carrier assembly member, in any order.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawing (i.e., left to right, right to left,etc.). Additionally, the first, second or third members of each gear setmay be counted “first” to “third” in any order in the drawing (i.e., topto bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the second memberof the second planetary gear set with the second member of the thirdplanetary gear set.

A second interconnecting member continuously connects the first memberof the second planetary gear set with the first member of the thirdplanetary gear set.

The third member of the first planetary gear set is continuouslyconnected to a stationary member (transmission housing/casing). Theoutput member is continuously connected with the third member of thethird planetary gear set.

A first torque transmitting device, such a brake, selectively connectsthe second member of the second planetary gear set with a stationarymember (transmission housing/casing).

A second torque transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with the firstmember of the second planetary gear set.

A third torque transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with the inputmember.

A fourth torque transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with thethird member of the second planetary gear set.

A fifth torque transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with thefirst member of the second planetary gear set.

A sixth torque transmitting device, such as a clutch, selectivelyconnects the second member of the third planetary gear set with theinput member.

The six torque-transmitting mechanisms are selectively engageable incombinations of three to yield eight forward speed ratios and onereverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention; and

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes three planetary gear sets20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the ring gear member 34 and the sun gear member 32.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear arrangement also includes six torque-transmittingmechanisms 50, 52, 53, 54, 55 and 56. The torque-transmitting mechanism50 is a stationary-type torque-transmitting mechanism, commonly termedbrake or reaction clutch. The torque-transmitting mechanisms 52, 53, 54,55 and 56 are rotating-type torque-transmitting mechanisms, commonlytermed clutches.

The output member 19 is continuously connected with the ring gear member44 of the planetary gear set 40. The first interconnecting member 70continuously connects the planet carrier assembly member 36 of theplanetary gear set 30 with the planet carrier assembly member 46 of theplanetary gear set 40. A second interconnecting member 72 continuouslyconnects the sun gear member 32 of the planetary gear set 30 with thesun gear member 42 of the planetary gear set 40. The ring gear member 24is continuously connected with the transmission housing 60.

A first torque transmitting device, such as brake 50, selectivelyconnects the carrier 36 of the planetary gear set 30 and the carrier 46of the planetary gear set 40 via interconnecting member 70 with thetransmission housing 60. A second torque transmitting device, such asclutch 52, selectively connects the sun gear member 22 of the planetarygear set 20 with the sun gear member 32 of the planetary gear set 30. Athird torque transmitting device, such as input clutch 53, selectivelyconnects the sun gear member 22 of the planetary gear set 20 with theinput member 17. A fourth torque transmitting device, such as clutch 54,selectively connects the planet carrier assembly member 26 of theplanetary gear set 20 with the ring gear member 34 of the planetary gearset 30. A fifth torque transmitting device, such as clutch 55,selectively connects the planet carrier assembly member 26 of theplanetary gear set 20 with the sun gear member 32 of the planetary gearset 30. A sixth torque transmitting device, such as input clutch 56,selectively connects the planet carrier assembly member 46 of theplanetary gear set 40 and the planet carrier assembly member 36 of theplanetary gear set 30 via interconnecting member 70 with the inputmember 17.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting mechanisms are selectively engaged incombinations of three to provide eight forward speed ratios and onereverse speed ratio all with single transition shifts with a doubleoverdrive.

The reverse (Reverse) speed ratio is established with the engagement ofthe brake 50 and the clutches 52, 53. The brake 50 engages the planetcarrier assembly member 36 and the planet carrier assembly member 46 viainterconnecting member 70 with the transmission housing 60. The clutch52 engages the sun gear member 22 with the sun gear member 32. Theclutch 53 engages the sun gear member 22 with the input member 17. Thesun gear member 22, sun gear member 32 and sun gear member 42 rotate atthe same speed as the input member 17. The ring gear member 24, planetcarrier assembly member 36 and planet carrier assembly member 46 do notrotate. The ring gear member 44 and output member 19 rotate at the samespeed. The speed of the ring gear member 44, and therefore the outputmember 19, is determined from the speed of the sun gear member 42 andthe ring gear/sun gear tooth ratio of the planetary gear set 40. Thenumerical value of the reverse speed ratio is determined utilizing thering gear/sun gear tooth ratios of the planetary gear set 40.

The first forward speed ratio is established with the engagement of thebrake 50 and the clutches 53, 54. The brake 50 engages the planetcarrier assembly member 36 and the planet carrier assembly member 46 viainterconnecting member 70 with the transmission housing 60. The clutch53 engages the sun gear member 22 with the input member 17. The clutch54 engages the planet carrier assembly member 26 with the ring gearmember 34. The sun gear member 22 rotates at the same speed as the inputmember 17. The ring gear member 24 does not rotate. The planet carrierassembly member 26 and ring gear member 34 rotate at the same speed. Thespeed of the planet carrier assembly member 26 is determined from thespeed of the sun gear member 22 and the ring gear/sun gear tooth ratioof the planetary gear set 20. The sun gear member 32 and sun gear member42 rotate at the same speed. The planet carrier assembly member 36 andplanet carrier assembly member 46 do not rotate. The speed of the sungear member 32 is determined from the speed of the ring gear member 34and the ring gear/sun gear tooth ratio of the planetary gear set 30. Thering gear member 44 and output member 19 rotate at the same speed. Thespeed of the ring gear member 44, and therefore the output member 19, isdetermined from the speed of the sun gear member 42 and the ringgear/sun gear tooth ratio of the planetary gear set 40. The numericalvalue of the first forward speed ratio is determined utilizing the ringgear/sun gear tooth ratios of the planetary gear sets 20, 30 and 40.

The second forward speed ratio is established with the engagement of theclutches 53, 54 and 55. The clutch 53 engages the sun gear member 22with the input member 17. The clutch 54 engages the planet carrierassembly member 26 with the ring gear member 34. The clutch 55 engagesthe planet carrier assembly member 26 with the sun gear member 32. Thesun gear member 22 rotates at the same speed as the input member 17. Thering gear member 24 does not rotate. The planet carrier assembly member26, planetary gear set 30, planetary gear set 40 and output member 19rotate at the same speed. The speed of the planet carrier assemblymember 26, and therefore the output member 19, is determined from thespeed of the sun gear member 22 and the ring gear/sun gear tooth ratioof the planetary gear set 20. The numerical value of the second forwardspeed ratio is determined utilizing the ring gear/sun gear tooth ratiosof the planetary gear set 20.

The third forward speed ratio is established with the engagement of theclutches 52, 53 and 54. The clutch 52 engages the sun gear member 22with the sun gear member 32. The clutch 53 engages the sun gear member22 with the input member 17. The clutch 54 engages the planet carrierassembly member 26 with the ring gear member 34. The sun gear member 22,sun gear member 32 and sun gear member 42 rotate at the same speed asthe input member 17. The ring gear member 24 does not rotate. The planetcarrier assembly member 26 and ring gear member 34 rotate at the samespeed. The speed of the planet carrier assembly member 26 is determinedfrom the speed of the sun gear member 22 and the ring gear/sun geartooth ratio of the planetary gear set 20. The planet carrier assemblymember 36 and planet carrier assembly member 46 rotate at the samespeed. The speed of the planet carrier assembly member 36 is determinedfrom the speed of the sun gear member 32, the speed of the ring gearmember 34 and the ring gear/sun gear tooth ratio of the planetary gearset 30. The ring gear member 44 and output member 19 rotate at the samespeed. The speed of the ring gear member 44, and therefore the outputmember 19, is determined from the speed of the sun gear member 42, thespeed of the planet carrier assembly member 46 and the ring gear/sungear tooth ratio of the planetary gear set 40. The numerical value ofthe third forward speed ratio is determined utilizing the ring gear/sungear tooth ratios of the planetary gear sets 20, 30 and 40.

The fourth forward speed ratio is established with the engagement of theclutches 53, 54 and 56. The clutch 53 engages the sun gear member 22with the input member 17. The clutch 54 engages the planet carrierassembly member 26 with the ring gear member 34. The clutch 56 engagesthe planet carrier assembly member 46 and planet carrier assembly member36 via interconnecting member 70 with the input member 17. The sun gearmember 22, planet carrier assembly member 36 and planet carrier assemblymember 46 rotate at the same speed as the input member 17. The ring gearmember 24 does not rotate. The planet carrier assembly member 26 andring gear member 34 rotate at the same speed. The speed of the planetcarrier assembly member 26 is determined from the speed of the sun gearmember 22 and the ring gear/sun gear tooth ratio of the planetary gearset 20. The sun gear member 32 and sun gear member 42 rotate at the samespeed. The speed of the sun gear member 32 is determined from the speedof the planet carrier assembly member 36, the speed of the ring gearmember 34 and the ring gear/sun gear tooth ratio of the planetary gearset 30. The ring gear member 44 and output member 19 rotate at the samespeed. The speed of the ring gear member 44, and therefore the outputmember 19, is determined from the speed of the sun gear member 42, thespeed of the planet carrier assembly member 46 and the ring gear/sungear tooth ratio of the planetary gear set 40. The numerical value ofthe fourth forward speed ratio is determined utilizing the ring gear/sungear tooth ratios of the planetary gear sets 20, 30 and 40.

The fifth forward speed ratio is established with the engagement of theclutches 52, 54 and 56. The clutch 52 engages the sun gear member 22with the sun gear member 32. The clutch 54 engages the planet carrierassembly member 26 with the ring gear member 34. The clutch 56 engagesthe planet carrier assembly member 36 and planet carrier assembly member46 via interconnecting member 70 with the input member 17. The ring gearmember 24 does not rotate. The planet carrier assembly member 26 andring gear member 34 rotate at the same speed. The sun gear member 22,sun gear member 32 and sun gear member 42 rotate at the same speed. Thespeed of the sun gear member 22 is determined from the speed of theplanet carrier assembly member 26 and the ring gear/sun gear tooth ratioof the planetary gear set 20. The planet carrier assembly member 36 andplanet carrier assembly member 46 rotate at the same speed as the inputmember 17. The speed of the ring gear member 34 is determined from thespeed of the planet carrier assembly member 36, the speed of the sungear member 32 and the ring gear/sun gear tooth ratio of the planetarygear set 30. The ring gear member 44 and output member 19 rotate at thesame speed. The speed of the ring gear member 44, and therefore theoutput member 19, is determined from the speed of the sun gear member42, the speed of the planet carrier assembly member 46 and the ringgear/sun gear tooth ratio of the planetary gear set 40. The numericalvalue of the fifth forward speed ratio is determined utilizing the ringgear/sun gear tooth ratios of the planetary gear sets 20, 30 and 40.

The sixth forward speed ratio is established with the engagement of theclutches 52, 53 and 56. In this configuration, the input member 17 isdirectly connected with the output member 19. The numerical value of thesixth forward speed ratio is 1.

The seventh forward speed ratio is established with the engagement ofthe clutches 53, 55, and 56. The clutch 53 engages the sun gear member22 with the input member 17. The clutch 55 engages the planet carrierassembly member 26 with the sun gear member 32. The clutch 56 engagesthe planet carrier assembly member 36 and planet carrier assembly member46 via interconnecting member 70 with the input member 17. The sun gearmember 22, planet carrier assembly member 36 and planet carrier assemblymember 46 rotate at the same speed as the input member 17. The ring gearmember 24 does not rotate. The planet carrier assembly member 26 andring gear member 34 rotate at the same speed. The speed of the planetcarrier assembly member 26 is determined from the speed of the sun gearmember 22 and the ring gear/sun gear tooth ratio of the planetary gearset 20. The sun gear member 32 and sun gear member 42 rotate at the samespeed. The ring gear member 44 and output member 19 rotate at the samespeed. The speed of the ring gear member 44, and therefore the outputmember 19, is determined from the speed of the sun gear member 42, thespeed of the planet carrier assembly member 46 and the ring gear/sungear tooth ratio of the planetary gear set 40. The numerical value ofthe seventh forward speed ratio is determined utilizing the ringgear/sun gear tooth ratios of the planetary gear sets 20 and 40.

The eighth forward speed ratio is established with the engagement of theclutches 52, 55 and 56. The clutch 52 engages the sun gear member 22with sun gear member 32. The clutch 55 engages the planet carrierassembly member 26 with the sun gear member 32. The clutch 56 engagesthe planet carrier assembly member 36 and planet carrier assembly member46 via interconnecting member 70 with the input member 17. The planetarygear set 20, sun gear member 32 and sun gear member 42 do not rotate.The planet carrier assembly member 36 and planet carrier assembly member46 rotate at the same speed as the input member. The ring gear member 44and output member 19 rotate at the same speed. The speed of the ringgear member 44, and therefore the output member 19, is determined fromthe speed of the planet carrier assembly member 46 and the ring gear/sungear tooth ratio/of the planetary gear set 40. The numerical value ofthe eighth forward speed ratio is determined utilizing the ring gear/sungear tooth ratios of the planetary gear set 40.

As set forth above, the engagement schedule for the torque-transmittingmechanisms is shown in the truth table of FIG. 1 b. This truth tablealso provides an example of speed ratios that are available utilizingthe ring gear/sun gear tooth ratios given by way of example in FIG. 1 b.The N_(R1)/S_(R1) value is the tooth ratio of the planetary gear set 20;the N_(R2)/S_(R2) value is the tooth ratio of the planetary gear set 30;and the N_(R3)/S_(R3) value is the tooth ratio of the planetary gear set40. Also, the chart of FIG. 1 b describes the ratio steps that areattained utilizing the sample of tooth ratios given for the engagementschedules of the above described transmission. For example, the stepratio between the first and second forward speed ratios is 1.52, whilethe step ratio between the reverse speed ratio (Reverse) and firstforward ratio is −0.48.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members; said input member being selectivelyinterconnected with at least one member of said planetary gear sets, andsaid output member being continuously interconnected with said thirdmember of said third planetary gear set; a first interconnecting membercontinuously connecting said second member of said second planetary gearset with said second member of said third planetary gear set; a secondinterconnecting member continuously connecting said first member of saidsecond planetary gear set with said first member of said third planetarygear set; said third member of said first planetary gear set beingcontinuously connected with a stationary member; a firsttorque-transmitting mechanism selectively connecting said second memberof said second planetary gear set with said stationary member; a secondtorque-transmitting mechanism selectively connecting said first memberof said first planetary gear set with said first member of said secondplanetary gear set; a third torque-transmitting mechanism selectivelyconnecting said first member of said first planetary gear set with saidinput member; a fourth torque-transmitting mechanism selectivelyconnecting said second member of said first planetary gear set with saidthird member of said second planetary gear set; a fifthtorque-transmitting mechanism selectively connecting said second memberof said first planetary gear set with said first member of said secondplanetary gear set; a sixth torque-transmitting mechanism selectivelyconnecting said second member of said third planetary gear set with saidinput member; said torque-transmitting mechanisms being engaged incombinations of three to establish eight forward speed ratios and onereverse speed ratio between said input member and said output member. 2.The transmission defined in claim 1, wherein said firsttorque-transmitting mechanism comprises a brake, and said second, third,fourth, fifth and sixth torque-transmitting mechanisms compriseclutches.
 3. The transmission of claim 1, wherein said first, second andthird members of said first, second and third planetary gear setscomprise a sun gear member, a planet carrier assembly member and a ringgear member, respectively.
 4. A multi-speed transmission comprising: aninput member; an output member; first, second and third planetary gearsets each having a sun gear member, planet carrier assembly member andring gear member; said output member being continuously interconnectedwith said ring gear member of said third planetary gear set; said ringgear member of said first planetary gear set being continuouslyconnected with a stationary member; a first interconnecting membercontinuously connecting said planet carrier assembly member of saidsecond planetary gear set with said planet carrier assembly member ofsaid third planetary gear set; a second interconnecting membercontinuously connecting said sun gear member of said second planetarygear set with said sun gear member of said third planetary gear set; afirst torque-transmitting mechanism selectively connecting said planetcarrier assembly member of said second planetary gear set with saidstationary member; a second torque-transmitting mechanism selectivelyconnecting said sun gear member of said first planetary gear set withsaid sun gear member of said second planetary gear set; a thirdtorque-transmitting mechanism selectively connecting said sun gearmember of said first planetary gear set with said input member; a fourthtorque-transmitting mechanism selectively connecting said planet carrierassembly member of said first planetary gear set with said ring gearmember of said second planetary gear set; a fifth torque-transmittingmechanism selectively connecting said planet carrier assembly member ofsaid first planetary gear set with said sun gear member of said secondplanetary gear set; a sixth torque-transmitting mechanism selectivelyconnecting said planet carrier assembly member of said third planetarygear set with said input member; said torque-transmitting mechanismsbeing engaged in combinations of three to establish eight forward speedratios and one reverse speed ratio between said input member and saidoutput member.